Patent GB-144438-A (GB)
Title: Improvements relating to the control of power absorbed in an electric furnace
IPC: H05B3/00
Filed: 1919-04-25
Abstract: 144,438. Campbell, D. F., Gifford, W. S., and Waite, H. S., (trading as Campbell, Gifford, & Waite), and Taylor, G. E. April 25, 1919. Master control systems; controllers, actuating. -A furnace regulator dependent both on the current and on the electric pressure between an electrode and a neutral point comprises a motor controlled by the fields of a number of stationary electro-magnets. As shown, these electro-magnets K<1>, K<2>, L', L<2> act on a soft-iron arm N attached to the shaft o of a motor controller of the tramway type. Current is directed to any one of the four or more electro-magnets, optionally, through relays J<1>, J<2>, M', M<2>, by a regulator H which may consist of an aluminium disk or drum acted on by the shaded poles of an electromagnet G in shunt to the bath and an electromagnet F receiving current from a transformer W in the circuit of the corresponding electrode; an adjustable resistance w shunts the transformer secondary. A spring T also acts on the disk H so that, when the furnace current is cut off, the motor is caused to raise the electrode. Insulated contact segments 4, 18 on the disk engage stationary contacts 31 when the current is high and the pressure low, and similarly-arranged contacts 43 - - 48 come into operation when the conditions are reversed. The contact segment 4 closes a circuit from an independent source I to the relay magnet J<1>. The armature of the magnet J<1> opens its own circuit through contact-segment 4 by means of a bridge 6, but this bridge also closes a parallel circuit through contact-segment 18, which engages its contacts before the segments 4; the effect of this arrangement is that the circuit is made by one segment and broken by the other segment. Also actuated by the armature of the first relay J<1> is a contact 21 closing a circuit through a coil U<1>, which, under control of dashpots V<1>, V<2>, opens the circuit through relay magnets J<1> at 11, simultaneously however closing circuit to an oppositely-acting coil D<2>. Thus the circuit of relay magnet J<1> is closed again after a short interval, and an intermittent current is sent through contacts 26 - - 28 to the first magnet K<1> of the motor controller. If the disk H moves further, it closes at 31 a circuit to the second relay magnet J<2>. This circuit includes a switch 34 operated by the motor current so that the relay cannot act and the controller cannot move from the first step to the second step until the motor current is normal. The second relay J<2>, when excited, breaks the first relay circuit at 7. The second relay has no device for opening its own circuit, so that a steady current is supplied to the motor in the second position in order to cause rapid motion of the electrode. Further relays and controller magnets may be provided for still more rapid movements. The connexions of the relays M<1>, M<2> and controller magnets L<1>, L<2> are similar to those of the relays J<1>, J<2> and magnets K<1>, K<2>. When operations of the controller by hand is desired, a handle X is moved downwards so as to engage a projection o<1> on the controller shaft, and simultaneously opens a switch 14 in the common return circuit of all the relay magnets J<1>, J<2>, M', M<2>.